import java.util.Scanner;

public class J6_2_1 {
    //求斐波那契数列的第n项。(迭代实现)
    public static void main(String[] args) {
        System.out.println("请输入n");
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int num = fib(n);
        System.out.println("第n项为"+ num);
    }
    public static int fib(int n){
        int f1=1;
        int f2=1;
        int f3=1;
        if(n == 1|| n ==2){
            return 1;
        }
        for(int i=3;i<=n;i++){
            f1=f2;
            f2=f3;
            f3=f1+f2;
        }
        return f3;
    }
}
